The present disclosure relates to an image forming apparatus which includes a sheet feeding portion for feeding sheets used for printing.
There are image forming apparatuses such as printers, multifunction peripherals, copiers and facsimile machines. The image forming apparatus stores sheets used for printing. For example, sheets for printing are set in a sheet cassette. Also, a roller for sending out (feeding) set sheets is provided. The roller wears as it is used. As wear advances, slipping becomes increasingly likely to occur. Slipping may cause a sheet feeding delay. When a slip so severe as to cause sheet feeding failure occurs, it is judged that a non-feed jam error has occurred. It is preferable to keep watch on the status of the roller so that the roller can be replaced before sheet feeding delays and errors frequently occur. There is one known example of a technology, as described below, which is related to watching the status of a machine.
Specifically, in a known image forming apparatus, an actual printing sheet arrival time sensed by a timing sensor provided on a sheet conveying path and a prescribed set time are compared with each other to judge conveyance quality; a deterioration judgement setting time calculated by subtracting from a setting time a minute time and the actual printing sheet arrival time are subjected to comparative judgement, and this comparative judgement is performed a prescribed number of times to count the number of times when the actual printing sheet arrival time is equal to or longer than the deterioration judgement setting time; when the number of times exceeds a prescribed number of times of judgement, warning information is displayed or is conveyed to a remote diagnosis system via, for example, a telephone line.
The sheet feeding roller makes contact with a sheet. The sheet feeding roller rotates to send out a sheet. That is, sheet feeding is performed using friction between a sheet and the roller that touches the sheet. Every time a sheet is fed, friction between the roller and a sheet recurs. Thus, the sheet feeding roller gradually wears. As the sheet feeding roller wears, the diameter of the roller decreases. As the period of use becomes longer, basically the friction force of the sheet feeding roller becomes smaller. While being used, the sheet feeding roller becomes increasingly prone to slip. The sheet feeding ability of the sheet feeding roller gradually lowers. As a result, the occurrence of sheet feeding delays increases.
Here, the behavior of sheets during sheet feeding changes depending on the remaining quantity of sheets. For example, depending on the remaining quantity of sheets, how sheets make contact with the sheet feeding roller (the state of contact) changes. When the remaining quantity of sheets is small, the sheets may need to be pulled up further than when the remaining quantity of sheets is large. Depending on the remaining quantity of sheets, the approach angle of sheets to a conveying member that follows the sheet feeding roller may change. As mentioned above, there is a problem that how likely sheet feeding delays are to occur is different depending on the remaining quantity of sheets. For example, when the remaining quantity of sheets is 5%, sheet feeding delays are more likely to occur than when it is 100%.
In the known technology mentioned above, the state of the roller is watched with no consideration given to the remaining quantity of sheets. Thus, it is not possible to solve the problem mentioned above.